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NIGERIAAn oil worker is covered in crude after a leak in the war zone that is the country's oil-rich Niger Delta. Forcing oil firms to clean up is a low priority amid an armed conflict that has gone on since the early 1990s.

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ROMANIADuring World War II, U.S. warplanes attempted to bomb the Ploiesti oil complex, one of Europe's most productive. The Nazis repelled them, in part by lighting the oil on fire. Ever since, Romania's capacity has consistently diminished. Most of the plants now refine, not extract, oil.

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The country has 3 percent of the world's known oil reserves, but vast swaths of unexplored territory. Born just 18 years ago with the Soviet breakup, the oil industry there now provides half the country's exports and a third of its GDP.